The present invention relates to a process for treating heavy hydrocarbons with water to form light hydrocarbons, a gaseous product and a residue. More particularly, the present invention is directed to a process for treating heavy hydrocarbons containing organometallics, for example vanadium and nickel, organosulfur and organonitrogen compounds, and asphaltenes with water at elevated temperatures and pressures, in the absence of externally added catalyst and hydrogen, for a time sufficient to form a light hydrocarbon product, substantially free of vanadium and nickel, a gaseous product and a residue.
There exist enormous quantities of heavy hydrocarbons such as heavy petroleum crude oils and tar sand bitumen (the heavy hydrocarbons extracted from tar sands), as well as residual heavy hydrocarbon fractions obtained from heavy hydrocarbon crudes such as atmospheric tower bottoms products, vacuum tower bottoms products, crude oil residuum and heavy vacuum gas oils. These heavy crude and residual hydrocarbon streams contain large amounts of organometallic compounds, especially those containing nickel and vanadium, organosulfur and organonitrogen compounds, and asphaltenes (high molecular weight polycyclic, pentane insoluble materials). In addition, these heavy crude and residual hydrocarbons are viscous and as such require a greater degree of processing to convert them into liquid materials that can be transported easily.
A number of alternate physical and chemical routes have been and are still being developed for converting heavy hydrocarbon materials into lighter liquid and gaseous fuels. Among the approaches are physical separation processes such as vacuum distillation, steam distillation, and solvent deasphalting, various thermal conversion processes such as visbreaking, delayed coking, fluid coking and coke gasification, catalytic processes such as hydrotreating, hydrorefining and hydrocracking, as well as multistage catalytic and noncatalytic processes. Each of these approaches has one or more drawbacks. In physical separation processes such as vacuum distillation, steam distillation and solvent deasphalting, a liquid hydrocarbon fraction is recovered in low yield but the asphaltene and resinous materials are not converted into product and must be disposed of separately. The various thermal conversion processes such as visbreaking, delayed coking, fluid coking and coke gasification require high temperatures above 500.degree. C. and generate a low quality by-product coke. In coke gasification, treatment of heavy hydrocarbons with steam and oxygen at high temperatures is necessary to produce a product gas, which must be utilized locally, and a limited yield of lighter liquid hydrocarbon product. Recently, a thermal conversion process called the Eureka process was disclosed in Chemical Engineering Progress, February 1981, pages 37-44 and in U.S. Pat. No. 4,242,196. The Eureka process converts petroleum residues, such as mixtures of vacuum residues from Khafij crude oil, or Iranian heavy crude oil, into a low sulfur petroleum oil and petroleum pitch by preheating the mixture of vacuum residues to about 450.degree. to 520.degree. C., feeding the preheated mixture to a fractionator and then to a charge heater at 500.degree. C. before stripping the thermally cracked low molecular weight hydrocarbons with superheated steam in a delayed coker reactor at 420.degree.-430.degree. C. under atmospheric pressure. Catalytic hydrogenation processes such as hydrotreating, hydrorefining, and hydrocracking may be used for converting heavy hydrocarbon feedstocks into a good quality material in high yield. However the hydrogenation catalyst employed in each of these processes is rapidly poisoned by the exceedingly large amounts of organometallic compounds and asphaltenic material in the heavy hydrocarbon feedstocks. The high levels of organometallic compounds in the feedstocks interfere considerably with the activity of the catalyst with respect to destructive removal of nitrogen and sulfur and oxygenated compounds such that the consumption of more than 3 kilograms of catalyst per 1000 kilograms of oil processed is normally required.
The prior art has also converted organic heavy hydrocarbons and other organic liquids to fuels by reaction with water. U.S. Pat. No. 4,113,446 (Modell et al.) discloses that liquid or solid organic materials can be converted into high BTU gas, with little or no formation of undesirable char or coke, when organic material is reacted with water at a temperature at or above the critical temperature of water and at or above the critical pressure of water to achieve the critical density of water. While U.S. Pat. No. 4,113,446 discloses that the process may be conducted either in the presence or absence of a catalyst, only gas and no liquid hydrocarbon fractions are recovered. International Publication No. WO 81/00855 (corresponding to U.S. patent application Ser. No. 079,534, filed Sept. 29, 1979 by M. Modell) discloses that organic solid or liquid material is admixed with water (in the region of the critical density of water, i.e., densities of water from 0.2 to 0.7 gms/cm.sup.3) at pressures from 200-2500 atmospheres and at temperatures from 374.degree. C. to at least about 450.degree. C. to restructure the organic materials to form useful volatile organic liquids.
U.S. Pat. No. 3,983,027 (McCollum et al.) discloses a process for cracking, desulfurizing and demetallizing heavy hydrocarbon feedstocks such as vacuum gas oil, tar sand oils and atmospheric residual oils to produce gases, liquids (heavy ends and light ends), and a solid residue by contacting the heavy hydrocarbons with a dense-water containing fluid at a temperature in the range of 349.degree. C. to 400.degree. C. (660.degree.-752.degree. F.) and at a pressure in the range of 2500 psig to 4400 psig in the absence of an externally supplied catalyst and hydrogen or other reducing gas. The density of water in the dense-water containing fluid was at least about 0.1 g/mL, and sufficient water was present to serve as an effective solvent for recovered liquids and gases. However, in the examples which disclose a process for removal of vanadium and nickel, straight tar sands having no more than 256 ppm of vanadium and nickel were treated with water at 400.degree. C. and 4100-4350 psig for at least one hour. To produce a hydrocarbon product having an API density of 21 and low (10 ppm) nickel and vanadium content, the presence of alundum balls in the reaction zone at 400.degree. C. and 4100 psig and extremely low flow rates (1 mL of tar sands and oil per hour) were required. In another example run under identical conditions except that the flow rate was 2 mL/hour, the hydrocarbon product had an API density of 17.8 and an unacceptably higher (77 ppm) nickel and vanadium content.
U.S. Pat. No. 2,135,332 (Gary) discloses a process for the cracking of relatively heavy oil, such as reduced crude, other heavy oils of residual nature or a heavy gas oil consisting principally of constituents boiling above 700.degree. F. to produce gases, liquids (lower boiling hydrocarbons of the gasoline range) and a solid or liquid residue including coke by admixing the heavy oil with a diluent such as steam, low boiling hydrocarbon gases or fixed gases at temperatures in the range of 650.degree.-975.degree. F. (343.degree.-524.degree. C.) and at pressures as low as 300 lbs/sq in, preferably in the neighborhood of 2,000-3,000 lbs/sq in. Gary discloses the admixture is treated in three coils in a furnace; the admixture is preheated to a temperature just below the cracking temperature, such as 650.degree.-700.degree. F. (343.degree.-371.degree. C.), followed by passing the preheated mixture to a zone wherein it is rapidly heated to a temperature in excess of 900.degree. F. (&gt;482.degree. C.) followed by heating in another portion of the furnace at a temperature below the cracking temperature wherein the desired conversion is carried to completion. The converted products from the furnace are passed through a pressure letdown valve and forwarded thence to an evaporator where vapors separate from a residue which may be solid coke or liquid. In the evaporator the residue is separated from the vapors and the vapors are forwarded to a fractionation zone to separate out the higher boiling components and recover liquid boiling in the gasoline range. Further, Gary discloses that coke is formed within the heating coil by conversion of heavy asphaltenes and viscous materials due to the higher temperature and prolonged heating within the heating zone, but that less coking difficulties are encountered within the heating coil when operating under his high temperature (&gt;480.degree. C.) and high pressure (2000-3000 psi) conditions than are encountered under low temperature, low pressure conditions. However, Gary does not suggest a method of converting heavy oil containing high metal values, e.g., nickel and vanadium, into a light hydrocarbon oil substantially free of such metal values.
In addition, there are various catalytic processes for treating heavy hydrocarbons with water with specific externally supplied catalyst systems and externally supplied hydrogen at specified temperatures above the critical temperature of water and at specified pressures, from below to above the critical pressure of water.